International trends of orthodontic publications: A bibliometric observational study of the last decade (2011-2020)

ABSTRACT Introduction: The number of published orthodontic studies has increased considerably over the past ten years. Objective: To analyze the bibliometric data of international orthodontic studies included in orthodontic journals encompassed by the Scopus database between 2011 and 2020, as well as to undertake data comparison between the period 2010-2015 and the period 2016-2020. Materials and methods: A retrospective search was conducted on 14 orthodontic journals included in the Scopus database from 2011 to 2020. Studies of both primary and secondary types were targeted by the search. The yearly number of studies published in the 14 journals, and the first 20 countries, institutions and their type (public/private), and authors, respectively, regarding publication volume, were presented. Results: Over the past ten years, the number of publications in the chosen journals reached 9200, where the American Journal of Orthodontics and Dentofacial Orthopedics and Angle Orthodontist topped the journal list, with 22% and 12% of the publications, respectively. Furthermore, the orthodontic publication volume showed a declining trend by the end of the decade (-9%), where academic/public institutions produced most of the orthodontic studies, and the US (20%), Brazil (17%), and South Korea (8%) topped the countries with the most orthodontic studies. A comparison of the two halves of the decade revealed that orthodontic research exhibited an increasing trend in developing nations, especially Egypt (104%), Saudi Arabia (88%), and Iran (83%). Conclusion: The orthodontic studies published in the chosen journals over the past ten years showed a dynamic change in yearly publication and ranking of countries, institutions, and authors.


INTRODUCTION
Scholarly publication undergoes continuous change with time, and has increased over the recent decades. 1 The continuous change in the bibliometric data of such publications (such as author characteristics, publication type, affiliation, and country of origin) can be described with bibliometric methods.
Such methods can shed light on the effects elicited by a particular domain, group of authors, and subjects, and identify studies of special significance in a particular research field.
There has been a marked rise in the number of orthodontic publications in recent times due to innovations in clinical procedures, applications, and techniques. 2,3 The bibliometric data of orthodontic studies have been the focus of a few bibliometric studies, with emphasis on distinct research questions, timeframe periods, databases, and journal breadth. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] For instance, the study by Tarazona-Alvarez et al 4 was concerned solely with the bibliometric data of lingual orthodontics studies, whereas other studies analyzed the bibliometric data of orthodontic studies conducted in particular parts of the world 15,18 or that adopted specific research designs, such as systematic reviews and/or randomized clinical trials. 3,17 Moreover, highly cited orthodontic studies were explored within particular intervals of recent decades. 7,9,20 Certain bibliometric studies concentrated on publications from a limited number of orthodontic journals 9,13,18,19 or database range. 3,6,14,18 However, the restrictions The majority of previous orthodontic bibliometric studies have used Web of Science database (WoS). 4,5,[7][8][9]16,19,20 As far as the author is aware, the bibliometrics of orthodontic studies published in the journals encompassed in Scopus database have never been investigated. Indeed, the Scopus database does not have the longevity of the WoS, having been created in 2004, but displays greater breadth. 21 Regarding orthodontic literature, WoS encompasses 13 orthodontic journals as of 2021, of which 50% were added since 2015. On the other hand, 17 orthodontic journals are contained in Scopus, and most were added before 2005. Thus, the Scopus database compared to the WoS is an optimum choice when conducting orthodontic bibliometric studies due to its inclusion of more orthodontic journals with a greater literature coverage.
Given the above considerations, the purpose of the present paper was to explore bibliometric data of international orthodontic studies publications in orthodontic journals included in the Scopus database in the period from 2011 to 2020, as well as to compare how the bibliometric data transformed dynamically between the two halves of the decade in question.

LITERATURE SEARCH STRATEGY
The paper adopted an observational research design to review international orthodontic studies published in the last ten years

ELIGIBILITY CRITERIA
Original and review studies published between 2011 and 2020 were included, but biographies, book reviews, book chapters, editorials, retractions, errata, and proceedings were excluded.

DATA EXTRACTION
The bibliometric data associated with the orthodontic studies were exported using the Scopus database's refine result' tool. This tool was used to extract the number of studies published every year during 2011-2020 and the number of studies published in every chosen journal, country, institution, and authors. The tool was also used to extract the proportion of narrative versus systematic reviews and the publication language of the retrieved studies. Furthermore, the 'view citation overview' tool of the Scopus database was employed to extract the citation data of all authors, including the rate of self-citation during 2011-2020.

RESULTS
The number of orthodontic publications included in the chosen journals in the last ten years was 9200. Of these, 8802 were articles and 398 were reviews. The reviews comprised two sub-types: systematic reviews (n = 327) and narrative reviews (n = 71). The language of the greatest proportion of articles (94%) was English, whilst 4% of articles were written in French and 1.5% in German. By contrast, articles written in Korean and Portuguese accounted for less than 0.5% of the overall publications. The source journal, year, country, institution, and author were the criteria used to organize the descriptive data pertaining to the orthodontic studies.

PUBLICATION JOURNAL
The number of publications in the chosen orthodontic journals over the past ten years is given in  However, other journals had either the same or a higher research output in the second half of the decade by comparison to the first. Figure 1A shows the yearly volume of orthodontic publications during 2011-2020, where the number of publications was 9% lower in 2020 than in 2011.

PUBLICATION YEAR
In 2017, the number of orthodontic publications was the same as in 2011,

PUBLICATION AUTHOR
The number of authors involved in the production of the publications in the chosen orthodontic journals over the last ten years was 11,957.
Co-authorship with at least one author was the norm in most of the studies. The first 20 authors with the greatest proportion of publications in the chosen orthodontic journals are provided in Table 4. The maximum number of studies (n = 144) was authored by Guilherme Janson, while the next   Table 4: The first 20 authors with the greatest proportion of publications in the chosen journals, as well as the proportion of citation, including self-citation, over the last ten years.   , PH  77  5  18  54  85  107  100  148  138  155  207  101  1118  10   10  Lombardo, L  72  1  3  10  10  13  43  63  83  77  102  57  462  17   11  Siciliani, G  68  0  2  9  17  20  45  72  80  84  111  58  498  14 12

DISCUSSION
Orthodontic studies proliferated in the past years. Bibliometric studies could be employed to observe how trends in publication changed dynamically. The bibliometric data associated with international orthodontic publications in orthodontic journals included in the Scopus database over the period between 2011 and 2020 were analyzed in the present paper. In addition, a comparison was conducted between the two halves of the decade in question about the transformations in bibliometric data. As far as the author is aware, this is the first paper to comprehensively explore the orthodontic studies published in journals encompassed in the Scopus database over the last ten years.
The bibliometrics of published orthodontic studies were analyzed in a number of Studies. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Of those studies, some focused on citation patterns or investigated subjects, 3,7,9,12,17,20 while other studies focused on the bibliometric data of orthodontic studies published only in limited orthodontic journals. 9,13,18,19 Thus, the current study chose 14 popular orthodontic journals encompassed in the Scopus database in the period between 2011 and 2020 to gain as broad a picture of orthodontic publication trends as possible. Furthermore, distortion of results was prevented by excluding journals that were included only partially in the Scopus database. As far as the publication country is concerned, this paper corroborated earlier investigations by finding that most published studies were produced in the US. 15,16,19 followed by Brazil, South Korea, Italy, and the UK. However, the paper differs from earlier investigations in the fact that discrepancies in chosen journals and time periods engendered variability in the number of studies and the ranking of the publication countries. 15,16,19 Furthermore, in partial agreement with earlier work, 8 Another point of consistency between this paper and earlier work is the finding that academic institutions produced most orthodontic studies. 8,16,17,19,24 According to Aura et al., 16 academic institutions generated 80% of the orthodontic studies published in the journals included in the Journal Citation Report from 2007 to 2017, while non-academic and private institutions showed a decreasing trend in orthodontic research output. 16 One explanation for such results could be the greater emphasis placed on intensification of orthodontic research programs and recruitment of well-qualified academics with ample research experience to attain the necessary funding. 6 The favorable effects of specialty program accreditations like the Network of Erasmus-Based European Orthodontic Postgraduate Programs could also elucidate the high number of orthodontic studies produced by academic institutions. 25 The current results also showed that the overall self-citation rate was 19.6%, corroborating what was previously reported in orthodontics, 16,26 dental, 27 and other medical fields. 28 According to Livas et al. 26 , author origin and gender were strong contributors to the self-citation rate, where Asian authors and females were less likely to cite themselves than other regions and male authors.
In the present study, the self-citation rate of the first 20 authors was registered (Table 4), but no intention was put to profoundly investigate the self-citation pattern since most authors publish studies in other journals/fields, which could lead to inaccurate interpretation and comparison with other studies. The present paper is not without shortcomings, such as the limitation of the number of orthodontic journals to just 14.
Journals covering a wide variety of disciplines have started to proliferate, 29 with 287 such journals have been founded by the MDPI publisher, as an example. Over the past ten years, MDPI publications have increased annually, with around 110,000 articles being published just in 2019. 12 Hence, it is highly likely that studies on the topic of orthodontics could have been included in those journals. At the same time, it could be challenging to differentiate articles related to specialties from articles without any particular specialty. The journals examined in this paper were chosen specifically to capture as many orthodontic studies as possible while screening out non-specialty studies.
Nevertheless, open access journals with wide coverage should be included in future research in order to better understand the pattern of published orthodontic studies.